REPORT OF AN EXTERNAL REVIEW PANEL COMPRISED OF:
Dr. Markus J. Peterson, Texas A&M University, College Station, Texas
Dr. Michael D. Samuel, National Wildlife Health Center, U.S. Geological Survey, Madison, Wisconsin
Dr. Victor F. Nettles, Jr., Wildlife Health Associates, Dillon, Montana
Dr. Gary Wobeser, Canadian Cooperative Wildlife Health Centre, University of Saskatchewan, Saskatoon, Saskatchewan
Dr. William D. Hueston, Center for Animal Health and Food Safety, University of Minnesota, St. Paul, Minnesota
Chronic Wasting Disease (CWD) has been recognized in free-ranging cervids in Colorado since 1981, but how long it has been present or how it arose are unknown. More is currently known about the distribution and ecology of the disease in Colorado than in any other jurisdiction in North America. The Colorado Division of Wildlife must be commended for their leadership and diligence in investigating the disease, and for providing information and education about CWD to the public. There is little experience from elsewhere that can be used to guide management of this disease. In fact, efforts made by the Colorado Division of Wildlife serve as models for other wildlife regulatory agencies. The disease is significant because it decreases the perceived value of wild cervids, is a mortality factor that may impact cervid population dynamics, it can be spread to new areas through human activities, and there is no evidence that CWD will spontaneously disappear or be controlled without management intervention. Because there is little scientific knowledge about many aspects of CWD ecology, attempted intervention is certain to be controversial. Thus, management of CWD must be experimental and adaptive; it must integrate research, management, and surveillance programs to enhance the capability to control this disease. The best available scientific information should be used to plan management actions, and these programs must include methods for assessing the effectiveness of each aspect of the management plan. As new information becomes available, and as results of intervention activities are assessed, management techniques should be adjusted or replaced accordingly. The effectiveness of management can only be assessed based on changes in distribution and prevalence of the disease. For this reason, rigorous on-going surveillance must be an integral part of any CWD management plan.
The Colorado Wildlife Commission policy on CWD provides a suitable framework for management of the disease based on two objectives: 1) minimizing spread of the disease and 2) reducing prevalence in endemic areas. The goals of these objectives are to contain the disease and to reduce potential population impacts within the endemic areas. However, based on recent disease recognition on the western slope of Colorado (and in other states and provinces), it seems likely that new disease outbreaks will be discovered. Therefore, a third objective of eliminating the disease, when it is found outside the endemic area, also should be included in the policy. This objective should be coupled with a rigorous surveillance program for early detection of disease in new areas. General written management plans should be developed that describe the management options available for use in various situations. In addition, these plans should include their rationale and the methods that will be used to assess the effectiveness of management. These general plans would form the basis for detailed management plans at the Data Analysis Unit or Game Management Unit (GMU) level.
Methods that have been developed for CWD surveillance in endemic areas are generally suitable; however, more emphasis should be placed on collection of spatially explicit data that can be used to better define the apparent clumped distribution of the disease. Surveillance must be continued over time and sample sizes must be sufficient to detect changes in prevalence and distribution of the disease. Surveillance methods for effectively monitoring CWD-free areas to provide reliable early detection of disease and for determining the spatial distribution of disease need further development for use in Colorado and in other jurisdictions. An important adjunct to surveillance is continued research to define biological population units of deer and elk and to delimit their annual and seasonal distribution. Use of hunter-killed animals should be continued as a primary method of surveillance, but it is important that the Division have the authority to conduct intensive collections where inadequate samples are available from hunters and if infected animals are discovered outside the endemic areas.
Immunohistological testing of brain tissue should remain the standard for identification of infected animals until better or more rapid tests are developed and validated. Immunohistologic testing of tonsil and retropharyngeal lymph nodes is suitable for deer, and can be valuable in determining early infection status. However, these tissues lack sufficient sensitivity to detect infected elk. The Division should collaborate with other agencies to develop new, more rapid diagnostic tests. These must be validated through comparison with inmmunohistology before being used diagnostically. The Division should not become involved in provision of routine diagnostic tests for CWD except as required for management and research purposes, but should develop procedures to obtain all diagnostic results at no cost and in a timely manner from other laboratories that test for CWD in wild cervids in Colorado. The Division of Wildlife has been a leader in research on CWD in wild cervids since the discovery of the disease. Research staff within the Division should be commended for the quality and number of scientific publications on CWD; Division policy should encourage the publication of research results to increase the scientific knowledge on CWD and to assess management programs in Colorado. It is anticipated that additional new resources will become available that will enhance the Division’s involvement in CWD research. The Panel strongly recommends that these efforts target knowledge required for disease management in free-ranging cervids in Colorado. This should include the influence of animal density, demography, movement, and behaviour on distribution of the disease, methods of transmission, persistence of infectivity in the environment, and characterization of “hot spots”. New information on spatial distribution, transmission dynamics, population density, and demography should be used to update models of disease ecology. Colorado should work with other jurisdictions to develop coordinated studies of the epidemiology of CWD and of the effectiveness of various management approaches in different physiographic regions.
As discussed earlier, management of CWD in wild cervids must be experimental and adaptive, because of scientific uncertainties associated with the disease. Regulations preventing movement of live animals from endemic areas and feeding or baiting of cervids should be continued. Regulations should be developed to control the movement of carcasses and parts of cervids from the endemic area and to provide for safe disposal of these materials. Clinically affected animals should be removed as part of surveillance. Experimental population reduction in GMU 9 should be completed and, if possible, replicated in at least one additional site to allow more rigorous comparison of the relationship between cervid density and CWD prevalence. It also is reasonable to cull animals in “hot-spots” to reduce potential exposure, and environmental contamination, as well as to collect information on the precise distribution of affected animals. Plans should be developed for the management of CWD cases recognized outside known endemic areas. Live capture and marking, testing, and culling of infected individuals may be useful for research purposes in areas where hunting and or random culling is not feasible. However, this approach is expensive and has limited potential as a management tool.
The Colorado Wildlife Commission must be credited for making effective education and communication with the general public about CWD a top priority, and particularly for providing scientific information on CWD to the public and to individuals who may wish to hunt in endemic areas. The panel believes that it is appropriate for the Division to maintain an active working relationship with public health experts in matters related to human health and safety and to work with these health experts to develop accurate education materials regarding risk so that science remains the major determinant of policy. The Division should work with other agencies to ensure that services are available for hunters who wish to have harvested animals tested for CWD.
The complete report may be viewed by going to the POLICY AND LEGISLATIVE section of this webiste. Click on “Policy”, then click on “Review of Chronic Wasting Disease Management Policies and Programs in Colorado – Nov. 2002”.